1. Field of the Invention
The present invention relates to a cholesteric liquid crystal composition that reflects light having a particular wavelength range around room temperature and body temperature, and a use thereof.
2. Related Art
A cholesteric liquid crystal molecule has a helical structure in a liquid crystal state. Accordingly, upon irradiating a cholesteric liquid crystal phase with light, the liquid crystal phase reflects circularly polarized light having a specific wavelength range corresponding to the rotation direction and the pitch length of the helical structure of the liquid crystal molecule. For example, upon irradiating with visible light, the liquid crystal phase selectively reflects light having a wavelength of blue, green, yellow and red corresponding to the pitch length of the liquid crystal. The color of the reflected light has viewing angle dependency, i.e., changes depending on the viewing angle, which is different from a pigment or dye, which exhibits color by absorption of light. The cholesteric liquid crystal can be controlled in pitch length by the temperature and the species of the compound, and thus can selectively reflect light not only in the visible range but also in a near infrared range or an ultraviolet range.
Materials that selectively reflect light of various wavelengths within a wide wavelength range have been provided by utilizing the characteristics of the cholesteric liquid crystal. Examples of the materials include a liquid crystal pigment, a paint, a spray ink, a printing ink, cosmetics, an anticounterfeit printed matter and an ornament. Such materials have been proposed as an optical film, such as a polarizing plate, a compensation plate and a color filter, for an optical device, such as a liquid crystal display device and a holography device. The cholesteric liquid crystal pigment, which has been known in the art, includes a cholesteric liquid crystal polymer in a flake form and a microencapsulated cholesteric liquid crystal. JP-A-2001-311079 discloses manufacturing method of a microencapsulated cholesteric liquid crystal. Examples of the purpose thereof include a paint for an automobile and cosmetics.
An animal-derived material (cholesterol) extracted mainly from wool wax has been used as a raw material for the cholesteric liquid crystal (cholesteric material), and in recent years, a vegetable-derived material is receiving attention in view of care for the environment and the human body. The vegetable-derived material is a component extracted from vegetable seeds or various parts of vegetables, and can be obtained, for example, from rice bran, rice bran oil, soybean, wheat, corn, palm, cotton seeds, coleseed or the like. Examples of a vegetable-derived material that exhibits liquid crystallinity include vegetable cholesterol, which is contained in soybean in a large proportion, and a triterpene alcohol derivative, which is obtained from rice bran oil.
DD 252,884 discloses that a sitosterol derivative has a cholesteric phase in a region of 150° C. or more, and a composition thereof has a cholesteric phase around room temperature. The major component of the composition is a cholesterol derivative, to which the characteristics of the cholesterol derivative, i.e., exhibition of a cholesteric phase around room temperature, is reflected.
JP-A-3-99094 discloses that esterified products of triterpene alcohols have a cholesteric phase, but all the esterified products disclosed have a narrow region where a cholesteric phase is exhibited, and no compound is disclosed that has a cholesteric phase within a wide range around room temperature. The triterpene alcohols used therein are contained as mixtures in naturally-derived materials, and it is difficult to isolate them by extraction for industrial use.
JP-T-2004-504291 (the term “JP-T” as used herein means a published Japanese translation of a PCT patent application) discloses, as a vegetable unsaponifiable material, an ester of sterol, stanol or triterpene alcohol with a long-chain fatty acid. The compound is used in such purposes as cosmetics and pharmaceuticals, but JP-T-2004-504291 does not disclose or suggest liquid crystallinity.
JP-A-2006-176422 discloses that an ester of vegetable sterol or triterpene alcohol with a long-chain fatty acid, as a sterol ester obtained from rice bran, is used in such purposes as cosmetics and pharmaceuticals, but JP-A-2006-176422 does not disclose or suggest liquid crystallinity.
JP-A-5-310526 discloses γ-oryzanol, which is an ester of sterol or triterpene alcohol with ferulic acid, and JP-A-57-62212 discloses an esterified product of triterpene alcohol with hydroxybenzoic acid. However, these documents do not disclose or suggest liquid crystallinity.
In the case where a cholesteric material obtained from a vegetable-derived material is used in the cosmetic field, and particularly applied to the human lips and skin, such a material is demanded that exhibits cholesteric reflected color in a temperature range around room temperature or body temperature. Red to purple, preferably red to yellow colors are required to be developed in a temperature range in the vicinity of 0 to 60° C., particularly preferably 20 to 40° C. Accordingly, a cholesteric liquid crystal material is demanded to be controlled in color range with respect to temperature when the material is applied to the cosmetic field for exhibiting esthetic effect thereby.